Method for the production of extra-high strength galvanized wire

ABSTRACT

HIGH STRENGTH WIRE IS PRODUCED BY A SUITABLE COMBINATION OF ALLOYING ADDITIONS WITH DRAWING AND/OR PATENTING OPERATIONS. TO PREVENT SERIOUS LOSS OF STRENGTH IN THE LUBRICANT REMOVAL STAGE, AN ELECTROLYTIC CLEANING TREATMENT AT A CURRENT DENSITY OF 30-60 AMPS/IN.2 IS SUBSTITUTED FOR CONVENTIONAL LEAD CHARRING. FURTHER LOSSES IN STRENGTH ARE THEN PREVENTED THROUGH THE USE OF SHORTER THAN NORMAL IMMERSION TIMES IN ZINC SPELTER MAINTAINED AT A TEMPERATURE OF 820* TO 850*F. THE LATTER TREATMENT SERVES A DUAL FUNCTION IN TAT IS ALSO SUPPLIES ANY STRESS RELIEVING WHICH MAY BE REQUIRED.

United States Patent Office 3,814,675 Patented June 4, 1974 3,814,675 METHOD FOR THE PRODUCTION OF EXTRA- HIGH STRENGTH GALVANIZED WIRE Richard L. Sallo, Unity Township, Westmoreland County,

and Charles D. Stricker, Monroeville Borough, Pa.,

assignors to United States Steel Corporation No Drawing. Continuation-impart of application Ser. No.

30,358, Apr. 20, 1970, now Patent No. 3,668,090. This application Feb. 4, 1972, Ser. No. 223,732

The portion of the term of the patent subsequent to June 6, 1989, has been disclaimed Int. Cl. C23b 1/04 US. Cl. 204-445 R 4 Claims ABSTRACT OF THE DISCLOSURE High strength wire is produced by a suitable combination of alloying additions with drawing and/or patenting operations. To prevent serious loss of strength in the lubricant removal stage, an electrolytic cleaning treatment at a current density of 30-60 amps/in. is substituted for conventional lead charring. Further losses in strength are then prevented through the use of shorter than normal immersion times in zinc spelter maintained at a temperature of 820 to 850 F. The latter treatment serves a dual function in that it also supplies any stress relieving which may be required.

This application is a continuation-in-part of Ser. No. 30,358, filed Apr. 20, 1970, now Pat. No. 3,668,090.

This invention relates to a process for the hot-dip galvanizing of high strength wire and more specifically to such a process by which the serious loss of strength during the cleaning and coating operations may be prevented.

In order to provide an adherent, hot dipped coating of zinc on wire, it is essential that the wire surface be thoroughly cleaned. Thus, in commercial practice it has been necessary to remove the wire drawing lubricants by employing a lead charring procedure in which the harddrawn wire is passed through molten lead at temperatures of the order of 800 to 850 F. Surface oxides and traces of lime remaining from the drawing operation are then removed by pickling in hot HCl. The wire strands are then rinsed in water and then flux coated prior to passage into the molten zinc. As the wire emerges from the spelter, the excess molten zinc is removed, and the coating made uniform by means of a mechanical wipe, composed of either charcoal (for medium weight coatings) or asbestos (for lightweight coatings).

The aforesaid lead charring often serves a dual purpose in that it also anneals the hard, cold drawn wire. Unfortunately, the immersion times in the molten lead which are required to effectively clean the surface, result in severe losses in tensile strength, thereby precluding the production of galvanized Wire with extra-high tensile strengths, e.g. of about 275,000 p.s.i. and higher. The instant process overcomes this deficiency b substituting an electroalkaline cleaning process in which the strand is electrolyzed at a current density of from 30 to 60 amps/in. in an electrolyte containing alkali metal hydroxides, phosphates and carbonates in sufiicient proportion and concentration to provide a conductivity which will permit the passage of such high electrolyzing currents. The electrolyte is preferably maintained at a temperature of 160 to 210 F. and may contain a mixture of 60% to 80% NaOH, 5% to 30% Na4P O and 5% to 30% Na CO dissolved in water to a total concentration of from 8 to 20%. Subsequent to this cleaning procedure the wire is then HCl pickled, flux coated and zinc coated as in conventional galvanizing operations. However, to avoid the consequent loss in strength which would result in passage through the molten zinc, it is desirable to employ short immersion times in spelter maintained at temperatures somewhat lower than are now employed commercially. Since the immersion length of the zinc bath cannot be reduced indefinitely and nevertheless yield an effective coating, short immersion times can only be achieved, in a practical sense, by employing high line speeds, i.e. speeds in excess of 200 ft./min. However, effective wiping at such high line speeds is unattainable when employing conventional mechanical wipes (the coatings are rough and the weights cannot be controlled within specified limits). It is therefore desirable that the thickness and quality of the molten zinc coating be controlled by employment of a gas knife such as that disclosed in application Ser. No. 101,661 or US. Pat. 3,533,61, thereby permitting the use of line speeds within the preferred range of 200 to 400 f.p.m. At these high line speeds, depending on wire diameter, immersion lengths of from 3 to 15 feet have been found preferable for the purposes of this invention.

The following examples are illustrative of the advantages of the instant invention in producing high tensile strength galvanized wire. A -inch diameter rod containing points of carbon was M.H. patented by heating to 1725" F. and quenching into a lead bath maintained at 875 F. After acid pickling and borax coating, the rod was drawn to approximately reduction-in-area in six drafts to a final diameter of 0.118 inches. The wire so produced exhibited the following average mechanical properties:

Yield strength p.s.i 238,000 Tensile strength p.s.i 315,000 Reduction-in-area percent 5 1.2

Samples of this wire were cleaned and galvanized by the method of this invention. For comparison a control run was employed using standard commercial practices. Thus, the control sample A was lead charred at 810 F., HCl pickled, flux coated and then zinc coated at a line speed of 35 feet/min. in a spelter pan maintained at 835 F. Samples B through D were cleaned in accord with the method of Ser. No. 30,358. Thus, the wires were passed through an electrolytic cell consisting of 8 chambers, each 6 inches in length in which the polarity of the applied current was reversed in each chamber. A current density of 50 amperes/in. was applied to the strand through an aqueous alkaline electrolyte maintained at a temperature of 180 F. and containing, in weight percent, 8% NaOH, Na4P207 and NflgCOg- These samples were then similarly HCl pickled, flux coated and then zinc coated at 835 F. The resulting mechanical properties of the samples so treated are reported in Table I.

TABLE I Line speed Y. S. U.T.S. R/A

(f.p.m.) (p.s.i.) (p.s.i.) (percent) A (control) 35 223, 000 268, 000 46. 1 B nvent on) 200 219,000 282,500 45.5 C nvent on) 240 224, 000 285, 000 45. 3 D (invention) 300 229, 000 292, 000 45.1

the so cleaned strand and passage of said strand through a molten zinc bath and (d) wiping of the excess molten zinc to provide a uniform galvanized coating, an improved method for significantl reducing the loss in tensile strength attendant such a procedure, which comprises, removing said drawing lubricants by electrolyzing said strand with a direct current at a current density of 30 to 60 amperes/in. for an immersion period of at least about 0.4 seconds, in an aqueous alkaline electrolyte containing a solution of alkali metal hydroxides, phosphates and carbonates in sutficient proportion and concentration to provide an electrolyte conductivity which will permit the passage of said electrolyzing current.

2. The method of claim 1, in which said loss in tensile strength is further reduced by passing the strand at a rate of from 200 to 400 ft./min. through a molten zinc bath with an immersion length of from 3 to 15 feet, said bath being maintained at a temperature of about 820 F. to 850 F.

3. The method of claim 2, in which the electrolyte is 4 to Na P O, and 5% to 25% Na CO dissolved to a total concentration of about 8 to 20% 4. The method of claim 3, in which the polarity of the strand is reversed as it passes through a series of electrolytic treatment zones.

References Cited UNITED STATES PATENTS 3,668,090 6/ 1972 Sallo et al. 204 3,468,695 9/ 1969 Federman 117-128 3,048,497 8/ 1962 M6ller 117-52 2,437,474 3/ 1948 'Or0zeo et al 204145 R 2,776,255 1/ 1957 Hammond et al. 204145 R 3,507,767 4/ 1970 Stricker 204145 R RALPH S. KENDALL, Primary Examiner M. W. BALL, Assistant Examiner US. Cl. X.R. 

